Activated charcoal filters are made available at many military installations, civilian defense installations and in many military vehicles, to be used in the event the occupants are exposed to toxic agents such as poisonous gases. Such filters, prior to installation and use, must be stored in hermetically-sealed containers to prevent degredation of the charcoal. After exposure to toxic agents, the charcoal filters become saturated and must be removed and replaced. In a prior art design presently in use, a pleated particulate flter and a charcoal gas filter were mounted within a permanent housing by means including an outer retaining cover and an inner retaining cover. The covers sealed and retained the separate filters in the housing and permitted replacement of the filters. After usage of the prior art filter unit, it was necessary to decontaminate the housing and covers before new filters were installed. Such procedure was time consuming and costly.